You can't stop them coming back Nanajulie they are the fruiting bodies of a mycelium that is in the ground. Did you mulch the fern bed last autumn? If so this is where the spores could have come from. Possibly time to teach your grand son not to touch anything in the garden without permission? There are likely to be several toxic plants there and the only way is for the child to learn not to touch.

i agree as yopu cant stop them now youve got them . youl have to be vigulent on snapping them off . as moon grower sais the mane plant for wqant of a better word lives underground and the mushrooms litteraly let millions of spores out very quickly .

Thanks, I will watch out for them! Is the compost heap the right place to dispose of them - will the spores end up in the compost?

Some mushrooms emit spores from beneath their caps - the best thing to do with them is to twist them off with a plastic bag over your hand, then fold the bag over and seal it and bin it in the ordinary rubbish.

Thanks Bamboo :)